Telephone system.



F. W, DUNBAR.

LPHONE SYSTEM.

Awucmfm mm MAY 2a, 1909, nsnswin MAY 21, 1912.

1,209,689. Patented Dee. 26,1916.

lll

'lfililll STATES PATENT OFFICE.

IFRANCQH v\7. DUNBAR, Ol? CHICAG, LLINOIS, .ASSIGNOR. BY NLESNE ASSIGNMENTS, T0 KBLLGG BJJITCHBGARD SUPPLY CMLEANY, A` CORITORATIN 0F ILLINOIS.

TELEPHQNE SYSTEM.

Specification ci Letters Estent.

Application filed May 2B, 1909, Serial No. 458,296. Rene-ved Muy 21. i912. Serial No. 698,83?.

lr it uno-sin that L lfnmx u: ll'. Dumme, u ulm-u i-i' the lvnltcd kilates., ,fi-siding; at i"lailvii busily lilt Gradi, Stull?y Uli llillluli, huw imruwl neu und useful liuprorements iu 'telephone Systems, ol whirl? the follow in;l i u slurriliiziliiui.

ilu: ui-wid iuwnliou relates to telephone sistem generally und more particularly to the i1-cuits aud apparatus by which the busy uml iilliconditions of :i telephone liuc are vsulilishcd aud tested und ringing current applied lo thc called-tol' line.

lu varri'iu; out uri' invention, l have ficiisml :sistem iu uliirh the busy test conuri'llun lu ilumultiple contacts ol a callingl iclclgliouc liiuis iwlialilisliml, where an :tutoululir mulch i iiiilalfi-yril, :is soon urs the su ilifla is ci in motion, and in which, upon establishing ,'oruirrtiou with the 4..al|e-l'l'o. liuc4 rillufr a lure' lmet: signal will lic transuu iwi uwallu railing; circuit, if the culled-- l'or liiube busy at he Liuic connection is saliluhx-il with it; or if the called line be idle, walling riurrut will not be applied to the izilluddui liuc u'ithfuit the intervention nl the operator. This ax'i'aiigcuii'iit rei'iuiree, lire-L ilu' insertion of the lilik-circuit plug; lulu a ,lach wl' the i-:ilieillor line, and then, il' the said lim be idle, the pressing ot n ruig-ini; ln-x' er other manually controlled derive to irritiert ringing.' current out over the raliccl liuc to signal the called-for party. lu rmuuwrrial operation, this sequence of operation is also preferred and it is to lncet [his preference oi" practice that I have der Used the present fuistclu.

The spccilir nature of tlul invention will lu lil-ut understood by reference to the :tcrolupauyiug drawing' and thc following de tailed description, while the scope of the invention will be particularly pointed out in the aiuwnded claims.

lu tlul drawing', l have illustrated an individual calling' line at the left, adapted to be conuerted by un intervening' link-circuit to ,i4 purty lim` at the right. the connection lullin-cn thi` culling line and the link-circuit beingestablished by an automatic switch, und that between the opposite end of the link-circuit und the called line beingr established nuiuually. At the substation, the usuel equipment ma;T be provided. transmitter l0 and induction coil 1l are included in a normally open conductive bridge of the liuc limbs iii, 1E, which is adapted to be closed by the mritclnhool; 14 upon the removal of the rcflreiverll. A normally closed bridge includes the call-bell 16 und the condenser l?. ln the case of party lines, the rall.-bells are tuned in accordance with the well-lumwn harmonic principle to respond only to rui-lent of4 definite frequencies supplied Ylriun proper generators at the central milice. ln the case of the called line, the second, third :nid Yfourth substation outtits are indicated by the leads l8-19, 20-2l, L12-2li.

At the centruiolliee, each lino l2, 13 has access to switch. mechanism, here illustrated us a traxeiing switch individual to the line and arranged to select the irst idle linie circuit ot :i niunber of link-circuits Whose calling culle are controlled by operators. In thc present instaure, l), S, L, designate the pnuiari secondary und .local wipers of a,

switch individual to the calling line, and. contauts fr, tu! fr', il, c, f, y, a', bf, 0 d', e', ,f g and u", Il, c", d", e", f, g, desi cuate the cooperating fixed contacts which l'orni terminals of the primary, secondary and local strands of the associated link-cin cuits. In the present instance, the primary, seconular)r and local strands 1:, S', L', of the rentar-ts d', d' and d, are the only strands illustrated. It will of course be understood that in practice, each of the fixedV contacts c, b, c, c, f, g, and their companions, would be similarly connected. In the present instaure also` just to the right of the switch having the wipers P, S and L, is a switch having' wipers l, S2, L, having associated bank contacts. It will be noted that the strands I", S', L" of the link-circuit illustrated are also connected to contacts of this switch. Although the link-circuit'here illustrated is connected to but two switches, it will be understood that in practice the same may be connected tio any desired numlier` according to the number of lines which it is desired to give access to this link-circuit. .Each switch is provided With a motor magnet MM and appropriate mechanism t not illustrated) for moving the Wipers over their associated fixed contacts. Each switch is also provided With oH-normal contacts (lN, which are operated upon the first Inovement of the switch from normal. A line rela LR,'a cut-oli relay CO, a private relay R, and a release relayv RR is provided for each iine and its associated switch. ln the present instance, jacks J, J', forming alternate connection terminals for the line l2, 13, are provided, so that thc line may he connected to manually.

In the link-circuit, the tip strand lr is provided with the usual tip relays TR, TR", and the interposed condenser 2l.' while the sleeve strand S' is provided with sleeve rclays SR, SR', and an interposed condenser 25. In addition, the link-circuit is provided with a busy rela BR, a llipllop relay FF, and a tip contro relay TC. A call lamp C, answering su ervisory lamp S3 and calling supervisory amp S' are also provide Busy back si nal transmitting means are illustrated at B and an. operators outfit is illustrated at O. Generators Gf', G2, G3, G* are ada ted to be brought into circuit with the cal ed line through the agency of the manual switch 26 and the contacts of the flip-flop relay FF. These generators, as hefore indicated, are arranged to supply current of diifer frequencies to selectively operate bells at t e suostions of each party line.

With this outline oi the apparatus employed in the system, the operation will be readily understood. Assuming that the party at the substation at the left desires to converse with the party: at the completely illustrated substation at the right, he will remove his receiver 14 and thereby complete a. circuit for his line relay LR which may he traced from the live or negative ole oi battory B, through relay LR, norma contact 2'? of tela CO, line limb 12, transmitter 10, swtchook 14, induction coil ll, lineY limb 13,- normal contact 28 of relay C0 to ground, or the common return of the battery. The energization of relay LR grounds its con tact 29 and thereby completes a circuit for private relay PR, which may he traced from ground at contact 29, through closed olinormal contact 30, normal contact 3l. of release relay RR, relay PR to the olgipositc pole of battery B. Relay llt` is thereby cnergized to place a buey test upon the test contacts of the jacks J, J', and start the switch Wipers. Normally, the test contacts of the jacks are connected through cut-olf relay CO and normal contact 32 of relay PR to ground. Upon the energization oi this relay, however, this connection to the Lest contacts is changed from ground to battery via alternate Contact 33 of' rela PR, normal contact 27 of relay C0, and re ay LR to the live pole of the battery il. Thus the busy test ls placed upon the connection terminals of the calling line soon as the relay PR is operated and the switch. thereby started. The starting circuit for the switch extends from the lire polo ci grouncll guarra tor G, which may be either an alternating or pulsating machine, through motor mag net MM and alternate contact to ground. The opening 'of normal contacts 33 and 34 oi relay PR` disconnects the Wipers P, S during their advance movement and thereby prevents interference With existing conversation through switch contacts over whose multiples said wipers may pass. Upon the first advance step of the switch, the contact 30 of the oli-normal switch ON is opened, but in the meantime the local wiper L, which is preferably provided with an enlarged contactiug end so as to engage one contact hei'ore disengaging the preceding, is moved into engagement with contact o. As illus trated, this Contact is not connected with the illustrated strand L', but if it be assumed that this contact is connected to a strand L' of some other link-circuit and that the linkcircuit is idle, then the switch would not advance farther but would remain in this po sition, leaving the contacts P, S and L in engagement with contacts a, a.' and a." of the selected link-circuit. However, if it be as sinned that the link-circuit, corresponding to contacts, a., o', a", is bus then strand L oi' that link-circuit will 'e connected to ground over some one of several circuits, as will hereinafter more fully appear. Aecordingly, the circuit of private relay PR will not bc'interrupted by the opening of oli-normal Contact 30, but will be continued through normal contact 38 of relay RR and alternate contact 35 of relay PR, wiper L, contact a, strand L', to ground. Thus the wipers P, S and L will he advanced to the second set ot contacts b, b', In. This open ation will continue until the wipers engage the contacts of an idle link-circuit. If it he assumed that the lrst idle link-circuit enr gaged is that illustrated, then the contacts S and L will he left in engagement with contacts (Z, rl', d" by reason of the interruption of the circuit of relay PR thus extended via strand L and normal contact of key 68 to the normali open contact G7 of relay Sli, as soon as sugli link-circuit-is encountered. The denergiaation of relay PR will co1nplete the talk'ng strands 12, 13 at contacts 33. 34, and w' l of course interrupt the circuit of motor magnet MM. It may also be noted that th first step of the switch closed olf-normal c ntact 39 to ground. This is for the purp se of completing a circuit for release relay tR, as will more fully appear later.

As Soonas llhe switch stops in engagement with the conta `cts. al, ri', ci, a circuit is completed through tlw sleeve supervisory relay Sli and the cumul' relay C() of the calling line. which muy be traced from the live pole ol' battery B, through relay SR, sleeve strand H'. eut-oil' relay C0 and normal cons-n-r li ol relayr PR to ground. The test or l. l (l sleeve rings oi the jacks J, J are thus con neeted to batter' B through the relay SR instead of relaluR, as they were before the release of relay PR, and relays SR and CO are both operated in series. At the same moment circuit was closed through the rela'ye C()4 and SR, a circuit-Was provided for theoperation of relay T R, via relay LR, normal contact 2T of relay CO, normal contact' 34, of relay PR, switch contact Pd, strand P', and'said relay TR, to `ground. Ifelay TR is thus initially energized at the same moment as is relay SR, thereby prei ventinar even a momentary closing of the 15 release circuit which will later be traced in detail. The 'operation of the relay C() pro vides a substitute path for the continued energization of relay TR, as follows: from battery B, through sleeve relay SR to the windingsr o relay UO, as previously traced, then in multiple circuit with the winding of relay C() via alternate contact 2S, line limb 13, induction coil ll at the substation, Switch-hook 14, transmittcrlll, line limb 12, wiper; P, contact nl, strand P, and said tip relay TR to ground. The opening of ncrmal contact 27 disconnects the line relay LR, and the closing.r of alternate contact 28 extends line limb lto the sleeve strand S ot' the link-circuit. The cnergization of both relays SR and TR prevents the operation of the answering supervisory signal S3 and the associated pilot relay PL. On the other hand, however,` pilot relay PL and calling;r lamp C are energized by the closing,r of a circuit extendingl from the live pole of battery B, through said relay PL', and lamp C, alternate contact -10 of relay TR, conductor 41 and normal contact l2-43, to ground! The operator, upon observinglr the display of the call lamp C, will depress her listening key LK to include her head receiver 44, condenser 45y and winding of the Ainduction coil 46 in bridge of the StrandsPS to learn the 'order of the callingr party." For such purpose', the `transmitter 47 may be supplied from battery B, through impedance coil 48, and the local talking circuit for the`transmittel will include the other winding of induction coil 46 and condenser 49. Upon 'learning the number of the desired `substation, the operator will Set the switch 26 so as to include the proper generator G', G2, G or G* in circuit to` actuate the bell of the calledorparty in case his telephone be upon a party lille, or in case the calleftfor party be on an individual line, theoperatorv will leave the switch 26 in aA position to 1nclude the `generator for the bell ofsuch line. She will then insert the calling'plug Pa into one ofthe jacks J', J of the called-for line.

In case such lineis in use, there will be a .potential on` the sleeve contact of the Jack diiferent frdmthat of ground. In case the line is ink service as a calling line, 4such por `above described. The cl sling ifg t 1 lthat the line he wishes is in use.

tential will be supplied by one of the busy test connections heretofore traced in connection with the calling line. It such line is in service as a called line, such busy test con nection will extend through the sleeve relay SR of that 4link-circuit which is used to establish connection to said line, alternate contact .56 andl normal contact 55, to thc sleeve contact of itsyplug l, and thence through the connection between tlul multiple jacks to the contact in question. li then the called line be busy, the insertion of the plug P into the jack, will causr a flow olE current from the sleeve contact of the jack, through. the upper winding of the busy relay .BIL conductor 5I) and normally closed contact 51-l to ground. Relay BR will thus be immediately energized without further act on the part ot' the operator. The opening of its contact 52 will open the tip strand and thereby prevent all possible connection of ringing' current to that side of the circuit. Alternate contact 53, closed by thc energize-- tion of relay Bh', will, however. bring the winding of sleeve relay SR' and the lower winding of relay BR into a circuit which will extend from the live pole of the battery side of the circuit, through the already oper- 9 ated cut-oil relay C() and normal Contact 32 of the busy called line., This will cause the operation of sleeve relay SR and the continued operation of the busy relay BR.

In case the switch of the busy line was in process of selecting an idle link-circuit, its cut-otl relay (1() would not be operated, because its circuit is then open at normal contact 32 of its relay PR. Under these conditions, the sleeve relay SR would continue to vibrate until the busy line had selected a link-circuit, whereupon its cut-oil relay C() would operate and provlide a locking winding Jr'or the sleeve relay SR'lthrough it, as of contact 54 of' relay SR does not bri i e ringing generator into circuit, since, as before pointed out, such circuit .is Vi1itenrupted at Contact 52.. The openingof cont `ct 55 of rela BR prevents the short-circuilzlng of the llower winding: of relay BR, which would otheras to transmit ,a characteristic busy signal to the calling party as an indica'on `to him uchmechanism includes an interruptor If in circuit with one 4Winding;` of an induction coil 58 and the battery B The secondary portion of this circuit includes the other Winding of imluction coil 58,'condenser 59, closed 'contact 57. the sleeve side ot" theilinlc-circuit, the sleeve side oi' the line circuitrL the receiver at the substation, the tip side of the Sii 4. .l 1.20am

line circuit and ground at any grounded point along that slde of the circuit, such as that at tip relay TR. The operation of the ringing key Rl( will be without effect because its circuit is now held o en at alternate contact 53. The operation o relay SR' has extinguished the calling lamp C by opening its circuit at normal contact l2-i3, and has closed the circuit of the called supervisory lamp S" from batter ,viasaid lamp, normal contact (i3 oi' relay R', and alternate contact 113 -oiE said relay SR to ground, thus lighting it. As soon as the calling subscriber, in response to the busy back signal, replaces his receiver, thus opening the circuit of thc tip relay TR, the calling supervisory si nal S3 will light over the following circuit: )attery B, supervisory pilot relay PL, said lamp S3, closed contact 100 and normal contact G9 to ground. The operator is thus advised that the link-circuit plug may be removed.

In case the called-for line is idle, the sleeve contacts of the jacks J, J will be free from potential and connected to ground through the cut-oli relay CO; and upon insorting the plug P3, there Will be no iiow of 4current through busyrelay BR and consequently it will remain inert. In fact, this operation will not result4 in the operation of any of the relays of the link-circuit or of the called line. To apply ringing current to the idle called line,the operator momentarily depresses the manually controlled switch or ringing key RK. This will close a circuit forthe sleeve relaySR from the live pole o f the battery B, through said relay, normal contact 53 of relay BR, and closed contact of ringing key RK to ground. The energization of relay SR will at once close a locki circuit for itself which may be traced froml the live pole of battery, through said relay SR', closed contact 56,'normal contact 55, plug and jack sleeve contacts and cut-off relay CO to ground at contact 32. The operation of cnt-oil" relay C0 will disconnect the line relay and the associated switch from the control oi the parties on that line. The openi'n of normalcontacts 4342-f1 of relay S will open the circuit of call lamp C and ca use its extingnis'hment, as before described, and will prevent the operation of relay BR by opening the circuit through itsupper winding. AAs soon as contact 54 of rela SR is closed. the connected generator G G2, (is, or G, will be intermittently connected to the tip side of the circuit throu h the backcontact 60 of the flip-,Hop relay-F al-ternatelywith the-callin .supervisory tip relay .Thus relay ,eA is in@ .Sense al.; 'rin ing* relay j--sinoe ltsooperatlonf applies rinH current to the line.4 Tracing; the ringing circa-it at the instant the `i1pilop con-tact" 60 is in the position illuatratexh` we find the circuit extends fromfthe particular generator G', G2, G, or G, in service, through swltch 26, back contact 60, closed contacts 54, 52 in the tip strand I", thence out over the tip side of the circuit, through the call-bells and condensers upon the )arty line, or the single call-bell and con cnser in case of an individual line, back over the 'sleeve side of the circuit to round via fthe two paths, one through cut-o relay CO, and the other th'rouh sleeve relay SR. If desired, the fiip op relay FF may be, as shown, normally mcluded in a closed circuit through the interruptor I and therefore continuously acting except when relay TC is energized.

As contact 60 of the Hip-flop relay is at tracted, it first disconnects the generator from the tip side of the circuit, then momen tarily grounds the tip side of the circuit through contact 60mm-(32, and finally connects the tip side of the circuit to ground through tip relay TR. The momentary grounding ot this side of the circuit through contact 62 permits the charged condensers upon the circuit to be partially discharged before the tip relay TR is brought into circuit. This avoids the possibilityY of the discharge of the condensers operating said relay TR. As long asthe receiver at the called station remains upon its hook, there is no conductive path for steady current between the line limbs and consequently relay TR will remain unenergized. As soon, however, as the called party removes his receiver and thereby completes such a conductive bridge, and as soon as Hiphop relay FF brings tip relay TR into circuit, said `relay will he energized. The circuit by which this relay is energized is the battery supply cir`.

cuit for the called station and extends from the live pole of the battery B, through relay SR lto the sleeve side of the circuit, thence y through the. substation, back over the tip side of the circuit, through contact 60-61 of -relay FF, and relay TR to ground. Prior to this operation' of relay TR', and subsequent to the operation of relay SR', su-

pervisory lamp S remains lighted by reason of a circuit from the live pole of the battery, throu h said lamp, normal contact 63 of relay R" and alternate contact 43 of relay SR to round. As soon as relay TR is energize this lamp is extinguished and tip control relay TC is energize over a circuit extending from the live pole of the battery,

throu h said relay, alternate contact 63 o'f R', and alternate contact 43 of relay of contact 64 g circuit for relay SR to ground. The clbsin otrelay TC completes a loc that) to its,` tornate' position disconnects the interrapter I', thereby discontinuing the interay through alternate contact 43 to'f fgl'iialu Y ,lf-and the `movement; of its contact `65 Said relay, maintains it energized, thereby disconnecting the generators und con'ipleting l the tip strand at contact (3U-(31. The operation of tip relay TR also completed, at contact 101, the sleeve strand of the linlccircuit.

The heavy lines indicate the talking' circuit thus established between the two substations. During conversation. both supervisory lamps remain unlighted. ,Replacing tbe rcceiver at the calling substation releases the tip relay TR and lights the supervisory lamp S3, as previously described. Replacing the receiver at the called substation releases the tip relay TR and lights the called supervisory lamp S* over the following circuit:

battery, said lamp S4, normal contact G3, alternate Contact 43 and ground. The tip control relay TC remains locked up via the` said alternate Contact 423 of the sleeve relay SR. Both supervisory lamps now being lighted, the operator will remove the plug l3 to cause the release oi= the apparatus to normal position.

The release is secured by disconnectingA condnctorL from ground and connecting it to battery. Prior to release and subsequent to the selection of the link-circuit, the said conductor L has-been maintained connected directly to ground for the purpose of rendering the link-circuit busy to other callinglr isuprev'ented from operatinghould, just nt oil`-nol'imi.l contact 39 to ground, whereby it l ,i

` this momentga wiper L of some other call ing switch, seeking an idle linkvcircuit. wipe over one of the multiple coIitn(.'-ts d, or`

should the sleeve relay SR operate quicker than the tip relay TR, thus momentarily connecting battery to the coniilurtor L. via

lamp C, normal contacts 4() and G6, alternate contact 67 and key 68. Immediately after selection, the ground is removed from conductor L at contact 29, but is provided instead at alternate contact (i9, via key 68, alternate Vcontact 67, normal contact GG, conductor 103and said alternate contact 69. Upon inserting the'pluir` lEl into a jack of the called line, relay SR operates, as previously described, whether theline bebusy or idle, and thus grounds conductor L at Vthe alternate contact 66. As relay SR re- `lfrlaiiifl's energized until the plug is removed, it willbe seen that conductor L is maintained 1f {roundcd and the release relay ltlt shortrircuited during the entire busy period of the link-circuit, thus causing seeking switches to pass by busy link-circuits without releasing,r them.

Upon the Withdrawal of the pluw l, in response to the disconnecting signal, either from the jack of a busy line or from thc jack of a line at the conclusion o'l1 conversation, the sleeve relay SR is released, thereby releasing busy relay BR in the caso oi' :i busy line, or the tip control. relay 'l.`(`\` and consequently the fiip-ilop relay FF, in theA case oi an idle line. The release of the sleeve relay SR also extends battery l5 via pilot relay PL', lamp (l, normal contact 4i() (now closed), conductor 103, normal Contact (jfl, alternate contact G7, key 68, conductor L', contact Ir-d", and normal Contact Sole-156, through the release relay RR and thence to ground via ofi-normal contact Ell), thus operating said release relay lill. 'lhe operation of relay RR closes circuit from battery l, through private relay PR to alternate con tact 38, thus placingr said relay Pl?! in inultiplc circuit with thc pilot relay lL and lamp (I, and in series uith the rch-.asn re-n lay RR. The resistance nl' the lamp C is sniliciently high to permit the operation of relay PR, whereby both it and relay Rit are maintained operated via the oilnorniupcontact 39, as above traced. The operation of relay PR. opens the circuit of the wipers l` S and L, thus releasing relays SR and CO and restoring the link-circuit to .its normal idle condition. lt also closes the circuit of the motor magnet MM, asr previously dcscribed, and the switch rotates its wipers to their normal position. Dui-'ng rotation, the `\\ipers l), S are maintained open atcontacts 34 and 33 for the purpose previously described, and wiper L is maintained open at normal contact 38 so as not to interfere with the circuits connected to contacts a, b, c, d, etc. On reachingr theI normal position,

Vthe circuit of relays PR and RR is opened at off-normal contact 39, whereby both release their arn'iatures, thus leaving the switch and calling line in normal idle position.

In case the line limbs 12, 13 of an idle line should have been accidentally or purposely crossed, as by a falling Wire or by permanently removing theV receiver, ain ldle linkcircuitfwould be selected as described, but the operator would secure no responseV and would then cause key 68 to be depressed, thus connecting conduetorL to battery via resistance 71, whereby the switch would be released as ,above described. On reachin normal, howeveig'the circuit of relays -I' and RR, instead of being opened by the openini,r of off-normal contact 39 as pre-A` viously described, would be continued. via -130 alternate contact 31, oE-normal lContact 30,

and contact 29 now maintained closed by the continued operation of line relay LR, due to the permanent cross on the line. The switch. would therefore continueto rotate, the relays PR and RR finding a closed circuit through either contact 39 or 30 ofthe olf-normal switchl This rotation of the switch continues until the trou-ble is correlated or located but no link-circuits are interfered with after the first selectionl and release, By this means, such troubles are y confined lto the line itself.

Keys 68 and 7 0 may preferably be located before the traffic manager or chief o crater. If key 70 be depressed, thus 'groun ing the strand L', the corresponding link-circuit is made artificially busy. The chief operator may therefore, by means of the keys-70, throw out of use one or more link-circuits terminating before any operator, and 'can therefore regulate and proportion the business handled by each operator according to their respective abilities. Thus each operators position may be equipped with ten link-circuits arranged in regular order with respect to the fixed contact points. 'on the various selective switches. A slxilled operator may be able to keep all ten iii eliicient servi while an operator of less skill may be ab e to handle efficiently the calls from but five or six. The wire chief will therefore render artificially busy, by means of one of the keys 70, tbe cords in excess of the number which can be efficiently handled by each operator.

Obviously, in carrying out my invention, certain alterations and modifications may be made in the circuits and apparatus without ,departing from the spirit and scope of my invention. I therefore do not Wish to be limited to the specific matter illustrated, but aim to cover, by the terms of the appended claims, all such alterations and, modifications..

What I claim as new and desire to secure by Letters Patent of the United Flates is t, 1. A telephone system comprising calling and called telephone lines, a linlgcircuxit and connection terminals fornnitingi;A said lines, means other than said lnk-circuiti-for rendering said called line busy. manually ck l/t'rolled means operative u on the connectionfif said link-circuit to sai called line whenl idle to transmit ringingcurrent over said called line,

and meansdependent upon the non-exercise of said manual control andupon the connection osaid link-circuit to saidcalled linel when busy to transmit a busy signal from said link circuit back over said calling line.

2. A telephone system comprising calling and called telephone lines, a link-circuit and connection! terminals for uniting said lines, othozte'rminals for said called line, other lirlilrirruits for connecting through said tcrniinlls tossaid called line, manually con- 4to said called line w trolled means for aplplying ringin current enever said rst link- 'circuit is connected to it While it stands disconnected from said other link-circuits,`and a busy back device for transmitting a busy signa back over said first link-circuit and thc calling line whenever said first link-circuit is connected to the calling line While it stands connected to one of said other linkcircuits and before said manual control has been lexercised. 3. A telephone system comprising callin and called telephone lines, a link-circuit and connect-ion terminals for uniting said lines, means for establishing other connections with Said called line, a ringing relay, manually controlled means for operating said ringing relay, a ringing current source connected by the operation of said ringing relay and. the connection of said link-circuit to said called line to supplyringing current to said called lii1e,-a busy relay operated in response to the connection of said link-circuit to said called line, when busy, before the operation of said manually controlled means, and a busy back device operated by said busy relay to send a busy signal from said link circuit over said calling line.

4. A telephone system comprising calling and called telephone lines,` a link-circuit and connection terminals for uniting said lines to establish a talking circuit, means for establishing other connections With saidv called line, means for supplying vringing current and a busy back signal, ringing and busy back connections extending to said link circuit, a pair of relaysjor controlling said connections, and an energizing 'circuit for one of said relays including-a portion of the talking circuit.`

5. A telephone system comprising calling and called telephone lines, a link-circuit and connection terminals for uniting said lines to establish a talking circuit, meansv for establishing other connections with said called line, means for supplying ringing current and a busy back signal, ringing and busy back connections, a pair of relays for controlling said connections, land an energizing circuit for both of relays including a portion of the talking circuit. V,

6.' A telephone system comprisingcalling and called telephone lines, a link-circuitand connection terminals for uniting said lines to establish a talking circuit, means for es tabl ishing other connections with said called line, means for supplying ringinglcurre'nt and a busy back signal, ringing and busy back connections, `a pair of relays jointly controlling.,r one of said connections and one,

solely controlling the other connection, and` an energizing circuit for one 'of said reand called telephone lines, a link-circuit and connection terminals for uniting said lines to establish a talking circuit, means 'for es-v tablishing other connections with. said called line, means for supplying ringing current and a busy bark signal, ringing and busy back connections, a pair oi relays jointly controlling one of said connections and one solely controlling the other connection, and an energizing circuit for both of said relays including a portion of the talking cirruit.

8. A telephone system comprising calling and called telephone lines, a link-circuit and connection terminals for uniting said lines to establish a talking circuit, means for establishing other connections with said called lille, means `for supplying ringing and a busy bark signal, ringing and busy back connections, a busy relay solely controlling the busy hack connections, a ringing relay controlling the ringing connections jointly with said busy relay, andan initial energiaing circuit for said busy relay including a` portion of the talking circuit:

i). A telephone system com prising calling and called telephone lines, a link-circuit and connection terminals for uniting said lines to establish a talking circuit, means for establishing other connections with said called line. means for' supplying ringing and a busy back signal, ringing and busy back connections, a busy relay solely controlling the busy back connections, a ringing relay controlling the ringing connections jointly with said busy relay, an initial energizing circuit for Said 'busy relay including a portion of the talking circuit, and a maintaining circuit for both relays including a portion of the talking circuit.

10. A telephone system comprising calling and-called telephone lines, a linkafircuit and connection terminals for uniting said lines to establish a talking circuit. means ifm' establishingr other mnnections with said called line, means for supplying ringir-ig and a busy back signal, ringingand busy back connections, a busy relay solely controlling the busy back connections, a riugingrclay controlling the ringing connections jointly with said busy relay, a local ycncrgiz/,ing cir-- cuit foi-.said ringing relay and a manual switch for controlling said circuit.

11. A telepl'ioieA system comprising ralling and called telephone lines. a 'linlccircuit and connectiontegninals for uniting said lines to establish a talking circuit, means for establishing other connections with said called line, means forsupplying ringing and a` busy backsignal, ringing and busy back connections. a busy relaysolcly controlling the busy back connections, a ringing relay controllinflr theiinging connections jointly with said tbusy r'eliay, a. local" energizing `circuit for said ringing relay, a manual switch for controlling said circuit, and a main taining circuit for said ringing relay including a portion of the talking circuit.

12. telephone system comprising calling and called telephone lines, a. link-cil`- cuit and connection terminals for uniting Said lines to establish a talking circuit, means for establishingr other connections with said called line, means for supplying ringing current and a busy back signahringing and busy back connections, a pair of relays for controlling said connections, a manual switch, and an energizing circuit for one of said relays including said switch and contacts of the other relay.

13.` A telephone system comprising calling and called telephone lilies, a linkmircuit and connection terminals for uniting said lines to establish a talking circuit, means for establishing other connections with said called line, means for supplying ringing current and a busy back signal, ringing and busy back connections, a pair oi relays jointly controlling one, of said connections and one solely controlling the other connection, a manual switch, and an energizing circuit for one of said relays including said switch and contacts of Athe other relay.

11. A telephone system comprising calling and called telephone lilies, a link-cir- .cult and connection terminals for uniting said lines to establish a talking circuit, means for establishing other connections with said called line, means for supplying ringing cm'rent and a busy back signal, ringingand busy back connections, a busy relay solely controlling the busy back connections, a ringing relay controlling the ringing connections jointly with said busy relay, a manual switch and an energizing circuit for one of said relays including said switch and contacts oi' the other relay.

l5. A telephone s vsten'i comprising ralliug and called telephonil'incs,'a link-cir cuit .aiulconnectioxi terminals for uniting vsaid lines to establish a talking circuit. ,means for establishing other connections with said called line, means for supplying ringing current and a busy back signal, ringing and busy back connections, a busy relay solely controlling the busy' hack connections. a. ringing relay controlling the ringing connections jointly with said busy relay, a manual switch, an energizing circuit 4for said ringing relay including said switch and contacts of said busy relay.

16. A telephone system comprising calling and called telephone lines. a` linkcir cuit and connection terminals for uniting said lines, means for establishing other connections with said called line, asource oi.

ringing current, va relay for connecting said V`source to the called line, a busy back signal transmitter, a busy relay for connecting ing current, a rclaly 1 said transmitter to the calling line and for breaking the ringing current connection to the called line, and a manual switch for encrgizing said first-mentioned relay when sald busy relay is inert.

17. A telephone system comprising calling and called telephone lines, a link-circuit and connection terminals for uniting said lines, means for establishing other connections with said called line, a source of ringfor connecting said source to the called ne, a. busy back signal transmitter, i a busy relay for connecting said transmitter to the calling line and at the same time operating said lirst-mentioned relay and interrupting the ringing current connection to the called line, and a manual switch -for energizing said first-mentioned relay when said busy relay is inert.

1S. A telephone system comprising calling and called telephone lines, a link-circuit and connection terminals for uniting said lines. a call-bell and condenser in normal bridge of the called line, a source ofringing current, a control relay adapted to operate u on the response of the called party, a ipfiop relay forv alternately connecting sald source and said relay to one limbof said line, and means for prdviding a discharge path for said condenser upon each operation of said flip-flop rel'y to prevent the `operation of said control relay by the discharge of said condenser. i

19. A telephone system comprising calling and called telephone lines, a lnk-circuit and connection terminals for uniting said lines, a call-bell and condenser in normal bridge of the called line, a source of ringing current. a control relay adapted to operate upon the response of the called party, ra flip-flop relay for alternately connecting said source and said relay to one limb of said line, and a ground connection closed by said {lip-flop relay after each disconnection of said source and before the connection ofviysaid contro-l relay to the line limb, whereby the operation of said control relay by the'liischarge from said condenser is'prevented. ,1,

v 20. In a telephone system, the c'inbination with a telephone line, of an operators linkcircuit having a normally open contact in the talking circuit and connected with said line, signal-actuating apparatus for said circuit in operative relation with said line, a relay adapted to be operated to terminate said relation, and a second relay adapted to be operated by'current over said telephone line and controlled 4by said relay for closing said normallyopen contact.

21. In a. telep one system, the combination with a telephone line,.of an operators link- -circuit having a normallyopen contact in thetalki circuit and connected with said line, s1 val-actuating apparatus for said circuit 1n operative relation with said lines,

tive or closing said normally open contact.

22. A telephone system comprising telephone lineas, two conductor manually operable link circuit and a non-numerical switch for interconnecting said lirios, and means included in said link circuit for applying the busy signal or ringing current from said link circuit to the terminals of the called line.

23. A telephone system comprising calling and called telephone lines', a link circuit for .uniting said lines, automatic means for interconnecting a calling line and an idle link circuit, means for rend Aring aglcallcd line busy, manually control ed meiis for said link circuit effective when said link circuit is vconnected to said called line when idle to transmit ringing current over the called line, and means effective irrespectivc4 of the exercise or non-exercise oi said manual con-V trol when connection is made to said called line when busy to transmit busy signal from said link circuit back over said calling line.

24. A tele hone system comprising telephone lines, ink circuits having manual terminals for connecting to said lines as called lines, automatic means for interconnecting a calling line andan idle one of said link circuits, a manual switch and circuit connections eii'ective when said link circuit is connected to a called line when idle to transmit ringing current over said called line, and means effective without the operation of said manual switch responsive to connection of said link circuit to a called line when busy to transmit a busy signal from said link circuit back over said calling line.

25. A telephone system comprising telephone lines, link circuits havin manually connected terminals for connecting to` said lines when called, `automatic switchesindividual to said lines for connecting' a calling line to an idle link circuit, means controlled through an automatic switch or a manual terminal for rendering the connected line busy, a manual switch and means operative upon the connection of a link circuit to a called line when idle to transmit ringing current thereover, and means dependent upon the non-exercise of said manual control and upon the connection of said link circuit to said called line when busy to transmit a busy signal from said link circuit back over said ca ling line.

26. A telephone system comprising calling and called telephone lines, automatic cans for connecting said calling lines with a idle link circuit, means other than said link circuit for rendering said called line busy, manually controlled vmeans operative upon the connection of said link circuit to a called line when idle to transmit ringing current over said called line, and means dependent upon the non exercise of said manual control and upon the connection of said link circuit to said called line when busy to transmit a, busy signal from said link circuit bek ovex` said calling line.

27. A telephone system comprising telephone lines, means including nen-numerical metallically controlled automatic switches and two-conductor manual link circuits for interconnecting seid linee` and means ineluded 1n said luik eircults for applylng the busy signal er ringing current from said link circuits te the terminals of the czxlwl 1 line.

In witness whereof, I hereunte eign mjy name this 25th day of May, 1909.

FRANCIS W'. DUNBAR. Witnesses CAROLYN WEBER,

G. 'WEBSTER 

